1. Field of the Invention
The present invention relates to a secondary battery module including a plurality of secondary cells.
2. Description of the Related Art
A lithium-ion cell has been known as a type of secondary cells and is used in the form of a battery pack, for example, to be mounted on an electric vehicle. Specifically, this type of battery pack has a cell row incorporated therein, and the cell row includes a plurality of cells.
The cell row weighs considerably, and therefore, each of the cells or the cell row as a whole needs to be securely fixed in position.
Also, especially in the case of the battery module of a battery pack mounted on an electric vehicle, not only vibrations produced during the travel of the electric vehicle but also heat radiated from the individual cells need to be taken into consideration. Thus, in the battery module, a space is provided between the adjacent cells. The individual cells are cooled by the air flowing through the spaces, so that the cells are prevented from being overheated. Also, even if a cell swells due to rise in the output voltage, the space serves to prevent the cell from contacting with its adjacent cell.
Where the cells are so arranged as to leave a space between the adjacent cells, it is necessary that the individual cells should be immovably held inside the battery module. To this end, the battery module disclosed in Patent Document 1 identified below has upper and lower members. The lower member has a plurality of chambers for accommodating the respective cells independently of one another, and the upper member has a plurality of push portions for pressing the cells accommodated in the chambers.    Patent Document 1: Japanese Laid-open Patent Publication No. H05-193366
In the battery module of Patent Document 1, however, the cells are merely pressed by the push portions of the upper member, and therefore, when the battery module is vibrated or applied with external force, the cells move inside the chambers.
The electrode terminals of every two adjacent cells are electrically connected by a busbar. If the cells move as stated above, undesirable tension acts upon the busbars due to the movement of the cells, possibly causing damage to the busbars or to the electrode terminals.
Meanwhile, if the output voltage of a lithium-ion cell rises above its allowable upper-limit value or drops below its allowable lower-limit value, the cell possibly deteriorates or fails to operate properly. Accordingly, it is desirable that this type of battery module should be provided with a monitoring device for monitoring the output voltage of the cell. Such monitoring device includes, for example, a printed wiring board and an arithmetic processing unit mounted on the wiring board. The arithmetic processing unit is electrically connected with the positive and negative electrode terminals of the individual cells to be input with the output voltages of the respective cells. Specifically, the positive and negative electrode terminals are electrically connected through respective monitoring terminals to the wiring of the printed wiring board.
If the cells move as stated above, however, the monitoring terminals and the wiring board are also applied with tension, and such tension causes damage to the monitoring terminals or the wiring board, that is, failure of the connection between the individual terminals and the arithmetic processing unit.
An object of the present invention is therefore to provide a secondary battery module which is capable of securely holding secondary cells with a fixed gap provided between adjacent cells and thereby preventing damage to positive and negative electrode terminals, busbars, monitoring terminals and the like.